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Corsair Dominator DDR2-1142 (PC2-9136) 4GB Kit

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As all high-frequency modules from Corsair, this kit supports EPP (additional information written in SPD to operate at higher frequencies). It should be mentioned here that EPP is not widely used these days (although two years have passed since this standard was published). EPP data can still be read only by motherboards on NVIDIA chipsets, including the latest products based on nForce 780a. Look for EPP options in BIOS in SLI-Ready Memory (although these settings have nothing to do with SLI graphics, it's just a bad marketing name). The other chipset manufacturers probably don't like this open but unofficial standard because JEDEC does not support this extension. However, unlike chipset manufacturers, memory makers are much more active about it. Memory modules with EPP support are offered by all leading manufacturers, including Kingston, OCZ, Transcend, and others.

From the users' point of view, EPP support is not radically important. On the face of it, an option to automatically select frequency, timings, and increased voltage looks logical (if a memory manufacturer sells such modules as DDR2-1234 and guarantees stable operation at this very frequency, let it specify necessary timings and voltages in SPD). But on the other hand, non-standard memory frequencies are not supported by all devices, it's often necessary to raise the bus clock to obtain them. It leads to CPU overclocking. In some cases it may require adjusting peripheral bus multipliers and CPU/chipset voltages. So, additional configuration may be required in some cases. Otherwise, your computer may read EPP automatically and fail to boot up or become unstable.

And if manual configuration is unavoidable (if you purchase overclocker memory modules, you usually know what to configure), you can always specify voltage and timings manually. It helps when these values are printed on stickers or packages of memory modules. And the main point - no matter how fast this memory module is, it must support standard frequencies and voltages, so that users could at least boot up their computers and enter BIOS. We haven't seen motherboards that would automatically read EPP data at the first startup. But let's see what values are written into EPP in these modules.

EPP Standard Description: DDR2 UDIMM Enhanced Performance Profiles, revision 01.

Parameter Byte(s) (bits) Value Interpretation
EPP Identifier String 99-101 4E566Dh EPP SPD Support
EPP Profile Type Identifier 102 B1h Full Profiles
Profile for Optimal Performance 103 (1:0) 01h Profile 1
Enabled Profiles 103 (7:4) 02h Profile 0: not available
Profile 1: available
Profile 1
Voltage Interface Level of this assembly 116 (6:0) 8Сh 2.1 V
Addr CMD rate 116 (7) 01h 2T
Cycle time (tCK) 121 1Dh 1.75 ns (571.4 MHz)
CAS# latency (tCL) 122 20h 5
Minimum RAS to CAS delay (tRCD) 123 23h 10.06 ns (5.75)
Minimum Row Precharge Time (tRP) 124 23h 10.06 ns (5.75)
Minimum Active to Precharge Time (tRAS) 125 1Ah 26.0 ns (15)
Write recovery time (tWR) 126 38h 14.0 ns (8.0)
SDRAM Device Minimum Active to Active/Auto Refresh Time (tRC) 127 26h 38.0 ns (21.7)

Engineers decided to use only one full profile, which describes "almost" the official recommended mode for maximum performance of these modules. That is, DDR2-1142 (1.75 ns cycle time, 571.4 MHz) and voltage (2.1 V) are specified correctly, but timings are fractional: 5-5.75-5.75-15, so they should be rounded up to 5-6-6-15. That's probably how they decided to soften the automatically selected mode relative to the recommendations for manual overclocking.

Unfortunately, the engineers did not add the second profile. It would have been more useful to add settings for DDR2-1066, which is supported by modern systems as the standard mode (that is it's available without increasing a bus clock or overclocking, just by setting a proper multiplier for this memory frequency). In our opinion, it makes much more sense to use EPP for such standard modes (de facto), which are not specified by JEDEC. It's because these modes can be used not only by overclockers, but also by common users, who want to squeeze maximum from their computers in the standard mode without learning how to choose timings and voltages.

Testbed configuration

  • Processors: AMD Phenom 9700 (Socket AM2+), 2.4 GHz (200x12), B2 stepping, TLB Patch is disabled in BIOS; AMD Phenom 9750 (Socket AM2+), 2.4 GHz (200x12), B3 stepping
  • Chipset: AMD 790FX
  • Motherboard: ASUS M3A32-MVP Deluxe, BIOS 1001

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